Capacitance sensing systems can sense electrical signals generated on electrodes that reflect changes in capacitance. Changes in capacitance can indicate a touch event (e.g., the proximity of an object to particular electrodes). Capacitive sense elements may be used to replace mechanical buttons, knobs, and other similar mechanical user interface controls. The use of a capacitive sense element allows for the elimination of complicated mechanical switches and buttons, providing reliable operation under harsh conditions. In addition, capacitive sense elements are widely used in modern customer applications, providing user interface options in existing products. Capacitive sense elements can range from a single button to a large number arranged in the form of a capacitive sense array for a touch-sensing surface.
Transparent touch screens that utilize capacitive sense arrays are widely applied in today's industrial and consumer markets. They can be found on cellular phones, GPS devices, set-top boxes, cameras, computer screens, MP3 players, digital tablets, and the like. The capacitive sense arrays work by measuring the capacitance of a capacitive sense element, and looking for a variation in capacitance indicating a touch or presence of a conductive object. When a conductive object (e.g., a finger, hand, or other object) comes into contact or close proximity with a capacitive sense element, the capacitance changes and the conductive object is detected. The capacitance changes of the capacitive touch sense elements can be measured by an electrical circuit. One or more touch locations can be further determined according to the capacitance changes of the capacitive touch sense elements.
On the other hand, touch locations of a non-conductive object cannot be determined as effectively and efficient as those of a conductive object. Moreover, there is a need to measure the magnitude of force associated with a touch by a conductive or non-conductive object.